This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.
Vibration control is an important aspect of vehicles and machinery. Uncontrolled vibration can result in unwanted wear and excessive noise in sensor data. In recent years, unmanned aerial vehicles (UAVs) have been increasingly used for information gathering, such as reconnaissance, surveillance, and target tracking, for both military and civil purposes. To acquire information, UAVs are generally equipped with various sophisticated sensors and instruments such as high-resolution imaging sensors, accelerometers, compasses, and gyros.
UAVs have lightweight, lightly damped, and flexible structures characterized by closely spaced vibration modes and low natural frequencies (usually just a few Hz). They also suffer from high-frequency vibrations due to the rotation of propellers and air friction. Vibration has been an important concern for onboard sensors and instruments fixed directly to the aerial vehicle chassis. Undesired vibration disturbances can severely degrade their performances. To minimize vibration disturbances to sensors and instruments on UAVs, an efficient vibration control method is needed. The currently existing vibration control methods can be commonly classified as either passive or active methods.
Passive vibration control methods usually use viscoelastic dampers, springs, shock absorbers, or structures with certain compliances to suppress undesired vibration disturbances. In one such approach, the vibration isolation device is essentially a rigid-link parallel manipulator with a damper mounted between rigid legs and the base platform. Passive approaches are relatively simple and straightforward in structure and thus, are inexpensive for construction and maintenance. However, passive vibration control methods are generally inefficient to control low frequency vibrations on UAVs. In addition, passive vibration control methods are normally designed to control a certain type of vibration with a specific frequency range. They are not adaptive to a dynamic vibration environment with low frequency vibrations as well as high frequency vibrations.
Unlike passive systems, active vibration control systems utilize sophisticated methods with active vibration control strategies. For example, one existing vibration control system for robotic arms incorporates active feedback control for actuators of a robotic arm to compensate the robotic arm's vibration. Another example is a vibration control system that controls the vibration of a payload moving by a robotic arm. The tension in a cable along with the robotic arm is actively controlled through a motor such that the vibration of a payload can be properly compensated.
While existing active vibration control systems and methods are more efficient in handling various vibrational disturbances by being able to control both low and high frequency vibrations, these systems are expensive, complex in both hardware and software, and are relatively heavy, which makes them inappropriate to be applied on UAVs with limited take-off weight.
Therefore, there is an unmet need for a novel approach to actively and adaptively control vibration on UAVs.